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    <title>work_group_reduce</title>
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    <div class="refentry">
      <a id="id-1"></a>
      <div class="titlepage"></div>
      <div xmlns="" class="refnamediv">
        <a xmlns="http://www.w3.org/1999/xhtml" id="work_group_reduce"></a>
        <h1>work_group_reduce</h1>
        <p>
            Return result of reduction operation for work-items in a work-group.
        </p>
      </div>
      <div class="refsynopsisdiv">
        <h2></h2>
        <div class="funcsynopsis">
          <table xmlns="" border="0" summary="Function synopsis" cellspacing="0" cellpadding="0">
            <tr valign="bottom">
              <td>
                <code xmlns="http://www.w3.org/1999/xhtml" class="funcdef">
                    gentype
                    <strong class="fsfunc">
                        work_group_reduce&lt;op&gt;
                    </strong>
                (</code>
                <td>gentype  <var xmlns="http://www.w3.org/1999/xhtml" class="pdparam">x</var><code>)</code></td>
              </td>
            </tr>
          </table>
        </div>
      </div>
      <div class="refsect1">
        <a id="description"></a>
        <h2>Description</h2>
        <p>
            Return result of reduction operation specified 
            by <span class="emphasis"><em>&lt;op&gt;</em></span> for all values of <code class="varname">x</code> 
            specified by work-items in a work-group.
        </p>
        <p>
        This built-in function must be encountered by 
        all work-items in a 
        work-group executing the kernel. We use the 
        generic type name gentype to indicate the 
        built-in data types <span class="type">half</span> (if the
        <a class="citerefentry" href="cl_khr_fp16.html"><span class="citerefentry"><span class="refentrytitle">cl_khr_fp16</span></span></a>
        extension is supported),
        <span class="type">int</span>, <span class="type">uint</span>, <span class="type">long</span>, 
        <span class="type">ulong</span>, <span class="type">float</span> or <span class="type">double</span> 
        (if double precision is supported) as the type 
        for the arguments.
    </p>
        <p>
        The <span class="emphasis"><em>&lt;op&gt;</em></span> in 
        <code class="function">work_group_reduce_<span class="emphasis"><em>&lt;op&gt;</em></span></code>, 
        <code class="function">work_group_scan_exclusive_<span class="emphasis"><em>&lt;op&gt;</em></span></code> and 
        <code class="function">work_group_scan_inclusive_<span class="emphasis"><em>&lt;op&gt;</em></span></code> 
        defines the operator and can be <code class="code">add</code>, <code class="code">min</code> or <code class="code">max</code>.
    </p>
        <p>
        The inclusive scan operation takes a binary operator <code class="code">op</code> 
        with an identity <code class="code">I</code> and <code class="code">n</code> (where 
        <code class="code">n</code> is the size of the work-group) elements 
        <code class="code">[a0, a1, ... an-1]</code> and returns 
        <code class="code">[a0, (a0 <span class="emphasis"><em>op</em></span> a1), ... (a0 <span class="emphasis"><em>op</em></span> a1 
        <span class="emphasis"><em>op</em></span> ... <span class="emphasis"><em>op</em></span> an-1)]</code>. 
        If &lt;<code class="code">op</code>&gt; = <code class="code">add</code>, the identity 
        <code class="code">I</code> is 0. If &lt;<code class="code">op</code>&gt; = <code class="code">min</code>, 
        the identity <code class="code">I</code> is <code class="constant">INT_MAX</code>, 
        <code class="constant">UINT_MAX</code>, <code class="constant">LONG_MAX</code>, 
        <code class="constant">ULONG_MAX</code>, for <span class="type">int</span>, 
        <span class="type">uint</span>, <span class="type">long</span>, <span class="type">ulong</span> types 
        and is <code class="code">+INF</code> for floating-point types. Similarly 
        if &lt;<code class="code">op</code>&gt; = max, the identity <code class="code">I</code> is 
        <code class="constant">INT_MIN</code>, 0, <code class="constant">LONG_MIN</code>, 
        0 and <code class="code">-INF</code>.
    </p>
        <p>
        Consider the following example:
    </p>
        <p>
</p>
        <div class="literallayout">
          <p>
            <code class="code"><br />
void foo(int *p)<br />
{<br />
    ... <br />
    int prefix_sum_val = work_group_scan_inclusive_add(<br />
              p[get_local_id(0)]);<br />
}</code>
          </p>
        </div>
        <p>
    </p>
        <p>
        For the example above, let's assume that the work-group 
        size is 8 and p points to the following 
        elements [3 1 7 0 4 1 6 3]. Work-item 0 calls 
        <code class="function">work_group_scan_inclusive_add</code> 
        with 3 and returns 3. Work-item 1 calls 
        <code class="function">work_group_scan_inclusive_add</code> with 1 and 
        returns 4. The full set of values returned by 
        <code class="function">work_group_scan_inclusive_add</code> 
        for work-items 0 ... 7 are [3 4 11 11 14 16 22 25].
    </p>
        <p>
        The exclusive scan operation takes a binary 
        associative operator <code class="varname">op</code> with an 
        identity <code class="code">I</code> and <code class="code">n</code>
        (where <code class="code">n</code> is the size of the work-group) 
        elements <code class="code">[a0, a1, ... an-1]</code> and returns <code class="code">[I, a0, 
        (a0 <span class="emphasis"><em>op</em></span> a1), ... (a0 <span class="emphasis"><em>op</em></span> a1 
        <span class="emphasis"><em>op</em></span> ... <span class="emphasis"><em>op</em></span> an-2)]</code>. For the 
        example above, the exclusive scan 
        add operation on the ordered set [3 1 7 0 4 1 6 3]
        would return [0 3 4 11 11 14 16 22].
    </p>
        <p>
        NOTE: The order of floating-point operations is not guaranteed for the
        <code class="function">work_group_reduce_<span class="emphasis"><em>&lt;op&gt;</em></span></code>, 
        <code class="function">work_group_scan_inclusive_<span class="emphasis"><em>&lt;op&gt;</em></span></code> and 
        <code class="function">work_group_scan_exclusive_<span class="emphasis"><em>&lt;op&gt;</em></span></code> 
        built-in functions that operate on <span class="type">half</span>, <span class="type">float</span> and 
        <span class="type">double</span> data types.
        The order of these floating-point operations is also non-deterministic 
        for a given workgroup.
    </p>
      </div>
      <div class="refsect1">
        <a id="specification"></a>
        <h2>Specification</h2>
        <p>
            <img src="pdficon_small1.gif" />

            <a href="https://www.khronos.org/registry/cl/specs/opencl-2.0-openclc.pdf#page=152" target="OpenCL Spec">OpenCL Specification</a>
        </p>
      </div>
      <div class="refsect1">
        <a id="seealso"></a>
        <h2>Also see</h2>
        <p>
            <a class="citerefentry" href="work_group_scan_exclusive.html"><span class="citerefentry"><span class="refentrytitle">work_group_scan_exclusive</span></span></a>,
            <a class="citerefentry" href="work_group_scan_inclusive.html"><span class="citerefentry"><span class="refentrytitle">work_group_scan_inclusive</span></span></a>
        </p>
      </div>
      <div xmlns="" class="refsect3" lang="en" xml:lang="en"><a xmlns="http://www.w3.org/1999/xhtml" id="Copyright"></a><h4 xmlns="http://www.w3.org/1999/xhtml"></h4><img xmlns="http://www.w3.org/1999/xhtml" src="KhronosLogo.jpg" /><p xmlns="http://www.w3.org/1999/xhtml"></p>Copyright © 2007-2013 The Khronos Group Inc.
Permission is hereby granted, free of charge, to any person obtaining a
copy of this software and/or associated documentation files (the
"Materials"), to deal in the Materials without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Materials, and to
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